Detailed studies of the adverse effects of airway pressure on cardiac function are planned in postoperative patients. Left ventricular dimensions will be measured with ultrasonic transducers, ventricular pressure will be obtained with a micromanometer, and cardiac output will be assessed with Doppler techniques. Our research group has extensive experience with this topic in laboratory animals, and initial data generated in patients indicate that different physiologic principles may be acting in patients with cardiopulmonary disease as compared to normal animal models. Therefore, detailed investigation in man is essential and is now feasible with recent methodologic improvements. The circulatory effects of several modes of ventilation will be tested: conventional ventilation with positive expiratory airway pressure, intermittent mandatory ventilation, high frequency ventilation, and pressure support ventilation. Potential beneficial effects of systolic synchronous high frequency ventilation will be explored. It is possible that optimal ventilatory support may vary depending on the pathologic situation. Physiologic data will allow general clinical guidelines to be generated in the pathologic setting, and these guidelines will be used to optimize circulatory dynamics in each patient. Finally, possible benefits of early endotracheal extubation will be evaluated in a controlled series of coronary bypass patients, and criteria for early extubation will be expanded as indicated by the results. The general objectives of this proposal are to improve the understanding of cardiopulmonary interactions and to develop methods of ventilatory management that least compromise postoperative cardiac output in a broad range of cardiac surgical patients.